The present invention relates to electrical power conversion systems. More specifically, the present invention relates to an ac-to-ac converter.
Many aircraft include electric drives, ac distribution systems and ac-to-ac converters. Typically, the ac-to-ac converter converts ac power from the distribution system to a frequency that is suitable for operating an ac electric drive.
Two basic types of converters are usually used to perform the ac-to-ac conversion in aircraft. The first type of converter includes a source-side inverter for converting ac source power to dc power and supplying the dc power to a dc link; a low-impedance dc link capacitor connected across the dc link for smoothing dc link voltage; and a drive-side inverter for converting the dc power on the dc link to ac power.
The dc link capacitor tends to be large and heavy. Moreover, both the source-side and drive-side inverters are switched at high frequencies, which leads to high switching losses.
The second type of converter includes a single so-called “matrix” inverter. The matrix inverter does not have a dc link or a dc link capacitor. However, the matrix inverter includes more switches than the first type of converter (for three-phase power conversion, a typical matrix inverter includes 50% more switches). The additional switches make the matrix inverter more expensive. Moreover, switching of the matrix inverter is more difficult to control due to the greater number of switches, and the switching logic is more complex.
It would be desirable to eliminate the dc link capacitor in the first type of converter. Eliminating the dc link capacitor would reduce the weight, which, in turn, would reduce aircraft fuel consumption and aircraft operating costs.
It would also be desirable to reduce the switching losses in the first type of converter. Simplifying the switching and reducing the switching frequency would reduce switching losses.